Replying to Drug test

I just finished my Launch drivers course and have to take a drug test this week. My friend had his today and said they don't test the temp because they ship it to Texas to get tested. I smoked weed regularly til about 5 days ago. It is on federal record I guess cause it's through the US Coast Guard. My plan was to get clean piss from a friend in a 16 oz plastic flask and tape it to my inner thigh with a toe warmer stuck to it as a just in case. I know there are several threads on this but none of them were very useful I am wondering if anyone else here has used this method or taken a drug test for any kind of vessel license.